1. Field of the Invention
The present invention relates to a semiconductor device with a protective film as a silicon nitride (SiN) film, and a method of manufacturing the same, and more particularly, to a semiconductor device to which a high voltage signal is applied as a control signal and a method of manufacturing the same.
2. Description of the Related Art
Various semiconductor devices, in which a final protective film is a SiN film, have been suggested. See Japanese Patent Kokai Publication No. 7-263547 (patent document 1) and Japanese Patent Kokai Publication No. 2010-16153 (patent document 2), for example. In general, as illustrated in FIG. 1, a lateral power metal-oxide-semiconductor field-effect transistor (MOSFET) 1 having a reduced surface field (RESURF) structure includes a P-type semiconductor substrate 11, which has an N+ drain region 13, a drain drift region (N-well region) 12, a P+ impurity region 15, a P-type body region 14 and an N+ source region 16; a field oxide film 17; a gate electrode 18; an interlayer dielectric film, i.e., inter layer dielectrics (ILD) 20; metal layers 21 and 22; and a SiN film 23 as a final protective film. When the semiconductor device is actually used, a high voltage is applied between a pad (not illustrated in the drawing) connected to the metal layer 21 and another pad (not illustrated in the drawing) connected to the metal layer 22.
However, in the conventional semiconductor device, when the semiconductor device is actually used and a high voltage is applied between the pads, a leakage current flows in a surface of the SiN film and negative charges are trapped in the surface of the SiN film. This is caused by that a large number of dangling bonds (incomplete bonds) occur in the surface of the SiN film and that the surface of the SiN film easily absorbes external water. By an influence of the negative charges trapped in the surface of the SiN film, a depletion layer may be formed under the field oxide film (channel). In this case, there is a problem that operational characteristics of the semiconductor device fluctuate.